The present invention relates to elastomeric bearings for oscillatory service, and more particularly to a hybrid elastomeric bearing which is also capable of operation as a slider bearing.
The bearing of the present invention is particularly suitable for uses such as hinge bearings for airframe control surfaces and hydrofoil flaps, although its usefulness is obviously not limited to these particular applications. Bearings in this type of service operate most of the time under relatively light load and with a small angle of oscillation which usually is of the order of .+-.5.degree.. During some part of the operational time, however, which may be about 10% of the total time, the bearings must operate under a high radial load and with a relatively large oscillatory angle of the order of .+-.25.degree. to 30.degree. or more. While these severe conditions may exist only for relatively short periods of time, the bearing must be capable of operation under these conditions.
Elastomeric bearings are often used for oscillatory service. Conventional bearings of this type, such as are shown, for example, in Brandon et al. U.S. Pat. No. 3,690,639, consist of a plurality of concentric layers of rubber or other elastomer separated by thin metal layers to provide a laminated structure. Such bearings have the advantage of virtually infinite wear life but have limited load capacity and relatively limited torsional or angular range even when many layers of elastomer are used. Under radial load, the elastomer deflects radially which causes it to deflect axially so that it protrudes at the ends of the bearing beyond the metal laminations. Since this protruding section is unsupported, it is the location of maximum stress concentration and the permissible load on the bearing is limited by the maximum stress that can be allowed in this location. Attempts have been made to axial deflection of the elastomer, as in the above-mentioned patent, but since the elastomer is essentially incompressible, this also limits the radial deflection and the load capacity and angular range are severely limited. For these reasons, elastomeric bearings have not been usable heretofore for the type of service described above, where the bearing must be capable of occasional or intermittent operation at high loads and through large angles. Conventional slider bearings designed for the most severe conditions that may occur have therefore been used even though most of the time this capacity is not needed.